Modern high-speed, high performance systems require good thermal management. High temperatures can shorten component life and limit performance. So good system thermal performance must be included at the start of any new design. The power density of circuits has been increasing as the size of electronics continues to shrink.
Heatsinks have been a traditional way to help semiconductor devices to dissipate heat into the environment. Such heatsinks are typically made of finned aluminum and their bases are thermally coupled to the substrate of the semiconductor device. Very often, the heatsink must be electrically isolated from the substrate of the semiconductor device, so mica insulators and silicon gel are used between the heatsink and the device to pass the heat but block electrical current. A measure of how well the heat is coupled through is called the thermal resistance. It commonly is expressed as the thermal resistance between the active junction of a device and the ambient air. Forcing an airflow over the fins of an aluminum heatsink improves efficiency, especially between the heatsink itself and the ambient air.
Attaching a heatsink to heat-generating devices is one of the most inexpensive ways to manage heat build up. Minimizing the thermal resistance between heatsinks and the components to be cooled is a fruitful technology for efficient heat removal.
Many types of prior art thermal interface materials have been developed over the years to improve the heat transfer from heat-generating devices to their cooling systems and heatsinks. But manufacturers use a variety of ways to report material thermal resistance, such confuse end-users.
The industry standard ASTM D5470 test method is used to characterize a wide assortment of thermal interface materials ranging from dry pads to greases. A disadvantage of this conventional technique is it requires constant operator intervention to obtain a set of meaningful data. For example, the operator must place the specimen between the fixtures, manually apply load and heat, ensure the load is properly maintained during the unsteady-state, determine when the test reached steady-state, record temperatures at steady-state, and repeat all the steps for the next pressure level. The results are operator dependent, and often not repeatable.
Many suppliers have also either modified or incorrectly applied the standard method in such a way that it is difficult for the end-users to compare the data. Some common problems include using undersized samples and incorrect measurement of variables. If samples of TIM material are cut smaller than the cross sectional area of the test apparatus, they are likely to spread under compression and change the contact area. This is often not accounted for. Measured values like temperature and heat flow are often incorrectly applied and can lead to very large errors in reported data.